L-丙氨酸在LiNO_3,NaNO_3,KNO_3和NaClO_4水溶液中的体积性质

Volumetric Properties of L-Alanine in Aqueous LiNO_3, NaNO_3, KNO_3 and NaClO_4 Solutions

利用Anton Paar DMA 55精密数字密度计测定了L-丙氨酸在LiNO3,NaNO3,KNO3和NaClO4水溶液中的密度,计算了L-丙氨酸的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积、理论水化数和体积作用系数.根据静电相互作用和结构水合作用模型讨论了阴离子和阳离子对迁移偏摩尔体积的影响.结果表明,L-丙氨酸在四种含氧酸盐水溶液中的迁移体积均为正值,并且随着盐浓度的增大而增大.L-丙氨酸两性离子端基和阴阳离子间的静电作用对迁移体积的贡献是主要的.静电作用削弱了两性离子带电中心对周围水分子的电致收缩效应,造成了理论水化数随溶液浓度的增加而减小.L-丙氨酸在NaNO3,KNO3和NaClO4水溶液中迁移体积的不同主要是由于静电作用的不同引起的,在LiNO3水溶液中迁移体积的“反常”是由于结构相互作用的影响较大所致.

Densities of L-alanine in aqueous LiNO3, NaNO3, KNO3 and NaC104 solutions have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes, limiting partial molar volumes and transfer partial molar volumes have been calculated. Hydration numbers and volumetric interaction coefficients for L-alanine were evaluated. The transfer partial molar volumes from water to oxacid salt solutions have been discussed in terms of electrostatic interaction and structural interaction. The results show that all the transfer partial molar volumes of L-alanine are positive and increase with the increasing concentration of salts. The reduction in the electrostriction with increasing concentration of salts was confirmed by the decreased hydration number. The contribution of electrostatic interaction to transfer partial molar volumes is predominant. Electrostatic interaction is responsible for the trends of transfer partial molar volumes in NaNO3, KNO3 and NaClO4 solutions, while in LiNO3 solutions the influence of structural interaction is prominent.